Some regulations, and in particular the European regulations, specify that a main beam shall comply with a well-determined photometric pattern, without putting any particular constraints on how such a beam is to be obtained. Thus, a main beam may be established, whenever required by a driver, by leaving the dipper beam headlight on and by juxtaposing a beam additional to the dipped beam, with said additional beam being substantially complementary to the dipped beam and being provided by an additional headlight.
A specific advantage of this type of solution is that during night driving the dipped beam headlight remains switched on permanently, thereby reducing fatigue in its filament and the inevitable loss of lifetime associated with such fatigue, with such fatigue normally arising because it is conventional practice for the dipped beam headlight to be switched off each time the main beam is switched on, and vice versa.
In addition, a considerable increase in light intensity is obtained since the power available from two lamps is being summed.
French patent 1 393 430 describes several embodiments of additional headlights of this type. In each of these embodiments, there is an axial filament lamp, a reflector, and a closure glass, optionally accompanied by masking elements for masking certain determined regions of the light flux emitted by the filament. The specific design of the filament, of the masking elements, and of the vertical deflection strips provided on the closure glass serves to obtain a beam which is effectively essentially complementary to a European type dipped beam (as recalled below).
However, regardless of the way in which it is embodied in practice, an additional headlight of this type suffers from at least one of the following considerable drawbacks:
the reflector includes surface discontinuities and is therefore difficult to manufacture using up to date techniques such as injection molding;
the masking elements which intercept a portion of the light flux emitted by the filament reduce the useful light yield from the additional headlight; and
the closure glass is required to deflect rays vertically through a considerable angle by means of its in-built prisms, thereby giving rise to excess glass thickness making the glass difficult to manufacture, and also giving rise to optical defects due to the considerable steps or undercuts in the surface of the glass.
Preferred embodiments of the present invention mitigate or eliminate these drawbacks of prior art additional headlights, and seek, in particular, to provide an additional headlight which does not include a masking element for masking the light flux emitted by the filament, thereby increasing the resulting light yield, whose closure glass has deflector prisms essentially solely for obtaining small horizontal deflection of a determined portion of the light rays, and, at least in some embodiments, whose reflector is easy to make by molding.